Method of extruding capacitor cases



Dec. 10, 1968 F, w D S ETAL 3,415,098

METHOD OF EXTRUDING CAPACITOR CASES Filed March 8, 1966 30 q E kl Q I050 I00 I50 200 250 TEMP. 'C.

INVENTDRS:

FRANKLIN W. DANIELS EDWARD A. BARLDW THEIR ATTORNEY.

United States Patent 3,415,098 METHOD OF EXTRUDING CAPACITOR CASESFranklin W. Daniels and Edward A. Barlow, Glens Falls,

N.Y., assignors to General Electric Company, a corporation of New YorkFiled Mar. 8, 1966, Ser. No. 532,684 2 Claims. (Cl. 72-267) ABSTRACT OFTHE DISCLOSURE A zinc alloy casing ofovate cross-section is extruded bythe combined use of a heated zinc alloy blank and a punch whose flatpunch face includes a pair of parallel grooves therein, parallel to thelonger axes of the crosssection with one groove on each side of thecenter of the punch face.

This invention relates to the extrusion of Zinc tubular articles, andmore particularly to the extrusion of zinc tubular articles of anoncircular cross-section.

The extrusion of zinc cups or containers of circular cross-section iswell known as shown in U.S. Patent No. 1,492,230, Towne. However, greatdifficulty has been encountered in extruding articles of an oval 0relliptical cross-section because of the tendency of the article towrinkle or split during extrusion. It is a principal object of theinvention to provide a method for extruding tubular corrosion resistantzinc articles of noncircular cross-section.

A further object of the invention is to provide a method of extrudingcorrosion resistant zinc capacitor cases of oval or ellipticalcross-section, capacitor cases of this shape having good advantage forsuch use.

In accordance with the stated objects it has been found that thesplitting or wrinkling of the Zinc articles extruded from a blank can beeliminated by heating the blank to a temperature below 150 C. andapplying a nonuniform pressure to the blank so that the resultant flowof material is uniform.

Further objects and advantages will be apparent as the followingdetailed specification and from the drawing wherein:

FIG. 1 is a perspective view of the capacitor case;

FIG. 2 is a perspective view, partly in section, of the blank andextruding tool pair; and

FIG. 3 is a chart showing the relationships between temperature andpressure and reject rate.

As shown in FIG. 1, this invention relates to the manufacture of acapacitor case 5 having a generally tubular shape closed at one end byan integral bottom portion 7 and provided with a flare 9 at its openother end, which flare 9 is for the purpose of mating with a covermember (not shown) to be sealed thereto. The bottom 7 and thecross-sectional shape of the case 5 are elliptical or oval with sidewall portions 11 of a large, or greater, radius curve and end wallportions 13 of a small, or lesser, radius curve. The Wall portions 11and 13 respectively intersect the minor and major axes of the ellipsedefining the cross-section of the case 5. Since as shown in the drawingthe side wall portions 11 may, in part, be planar, the use of the termelliptical with reference to the shape of the case will be understood toa general use, as distinguished from a precise geometric use.

The case 5 is extruded from a blank 15 (FIG. 2) of a corrosion resistantzinc alloy containing small amounts of copper and titanium to improveits creep strength. Preferably, this alloy consists essentially of 0.5%copper, 0.15% Ti. and the balance zinc. The blank 15 has an area andshape substantially corresponding to the bottom 7 of the case 5 and athickness determined by the wall thickness of the case to be formed andits height. For

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2 example, in manufacturing a case with a major axis of about 2.78'. aminor axis of about 1.78" havinga height of about 3.5" and a Wallthickness .of about .023 with a bottom thickness of about .035", a blankthickness of about .220" is required. The extrusion of the blank 15 maybeeffected by a ,tOol pair comprising a femaledie 17 and a male die orpunch 19 as illustratedsomewhat diagrammatically inFIG. 2- The die 17has an oval or elliptical cavity 21 corresponding to the shape of theoutside surface of capacitor case 5 and into which cavity the blank 15is fed. The punch 19 closes on the blank andv applies sufficientpressure thereto to cause the metal to flow along the walls of thecavity, the punch area andshape determining the amount of materialpermitted to flow and hence'the wall thickness of the case. Since thematerial flow is opposite in direction to the direction of theapplication of pressure by the punch 19, the extrusion herein referredto is more specifically identified as reverse extrusion.

While the extrusion may be theoretically effected at any temperature asillustrated by curve 23 of FIG. 3, in accordance with an importantfeature of the invention, the blank 15 is heated to temperature of atleast C. before placement in the die cavity 17 so as to reduce thepressure, necessary to effect material flow. However, in extrudingarticles of a noncircular shape, such as the capacitor case hereinreferred to, it has been discovered that the reject rate, that isproduction of defective cases, increases with increasing temperature asillustrated by curve 25. Therefore, the temperature of the blank uponplacement in the die must be kept below 150 C. and preferably the blankis pre-heated to approximately C.

Heating of the blank to a temperature in excess of C. generally resultedin splitting or wrinkling of the side walls 11 of the case, hence it isbelieved that one of the factors requiring a lower temperature is thenoncircular shape. With a small radius curve defining the end walls 13and a large radius curve defining the side walls 11 the fiow of materialis more restricted in the small radius curve area and the material flowtakes place more rapidly in the side wall area. As the side wall formsmore rapidly, differential stresses result and the material on the sidesof the case separates. Another explanation for the splitting is that thezinc alloy is extremely temperature-sensitive, and becomes very weak asits temperature is elevated. Thus, if the temperature is too high, thematerial becomes very weak as it travels along the side of the punch andany condition creating nonuniform fiow of the material, such asmisalignment of the punch with respect to the die, will cause shearstress and fracture.

To further eliminate the differential stresses, the application ofnonuniform pressure to the blank is preferred. Thus, recesses or grooves27 (FIG. 2) placed in the face of punch 19 have been found to provideuniformity of flow of material during extrusion. It will be noted thatthe grooves are adjacent the side walls 11 of the resultant case andextend parallel to the major axis thereof. Thus, it is believed thatgreater pressure is: applied to the material required to flow in therestricted flow areas of major axis intersecting end walls 13 whichresults in the fprming of the end walls at the same rate as the sidewalls.

While the effect of the recesses 27 has been explained in terms of theresultant pressures, it is thought to be possible that this method ofeffecting uniform flow of mate rial in the extruding of noncirculararticles might actually be occurring mcrely because of the differentialtime rates of flow or some other phenomena. Therefore, the use of theterm nonuniform pressure is herein intended to include nonuniform timerates of application of a uniform pressure or other phenomena.

By way of the specific example; the process in accordance with thepreferred embodiment of the invention takes place as follows. Blanks ofzinc alloy are placed in a tumbling barrel along with a lubricant, suchas lard, for a sufiicient time to coat the blanks with the lubricant.The lubricated blanks are heated to approximately 125 C. by feedingthrough a suitable oven or furnace, and then fed singly into the diecavity. The punch 19 in immediately actuated to apply non-uniformpressure to the blank and effect uniform flow of the walls of theresultant case. The case is then finished on a suitable metal cuttingand forming machine to trim the top edge and form the flare 9 thereon.

It will thus be seen that there is provided a new and useful process forextruding zinc articles of a noncircular cross-section and moreparticularly for extruding zinc capacitor cases of an elliptical or ovalcross-section. While the invention has been disclosed with reference tothe preferred embodiment thereof, it will be understood that theinvention is not limited to the particular details shown and describedbut may be varied within the spirit and scope of the appended claims.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A method of manufacturing a corrosionq'esistant tubular article ofnoncircular ovate cross-section having a major and minor axis comprisingthe steps of:

(a) lubricating a zinc alloy blank;

(b) heating said blank to a temperature of at least about 100 C. butless than about 150 C.;

(c) extruding said blank into the shape of the article by placing saidblank in a suitable die cavity and forcing a die therein having a fiatpunch face perpendicular to said tubular article; and

(d) providing uniform flow of said zinc alloy into the wall of saidarticle by channeling a proportional part of said zinc alloy in pluralelongated opposite cavities in said punch face;

(e) said cavities being parallel to the major axis of said ovatecross-section with one said cavity of each side of the center of saidpunch face, the said cavities being spaced within the perimeter of saidpunch face.

2. A method as recited in claim 1 wherein said zinc alloy consistsessentially of 0.5% copper, 0.15% titanium and the balance zinc and saidblank is heated to a temperature of approximately 125 C.

References Cited UNITED STATES PATENTS 935,900 10/1909 Frank 722711,492,230 4/1924 Towne 72 -267 2,080,399 5/1937 Deibel 72267 2,533,94212/1950 Jongedyk 72267 CHARLES W. LANHAM, Primary Examiner.

K. C. DECKER, Assistant Examiner.

